At the start of 2016, the town of Kaitaia, in New Zealand’s Far North—population 5,000—had just experienced the loss of six young people to suicide in quick succession. Nina Griffiths, a local high school student, was one of the grieving. Among those who took their lives was a close friend who had been a member of a youth peer-support group with her. “We’re a small community, so that touches...